A press of pressure cell type generally comprises a force-absorbing press body which defines a press chamber. In the upper part of the press chamber, a press plate and a diaphragm of rubber or another resilient material are arranged, which together form a pressure cell. The pressure cell communicates with a source of pressure and expands when a pressure medium is supplied. In the lower part of the press chamber, a structural support or a tray is arranged, which comprises a bottom plate having a tray frame. The tray supports a working tool or a forming tool, a workpiece, a mat of rubber or another resilient material, covering the forming tool and the workpiece.
Presses of pressure cell type are used, among other things, when forming sheet-shaped blanks, for example sheets of steel or aluminum, for short series products within the aircraft industry and the motor industry. The sheet is placed in the press in such a manner that one of its sides faces a forming tool. The resilient diaphragm is arranged on the other side of the sheet. A closed space between the diaphragm and the press plate located above the diaphragm constitutes the pressure cell and this space is filled during the forming process with a pressure medium. By pumping additional pressure medium into the pressure cell, the pressure is increased in the pressure cell and the resilient diaphragm is pressed during stretching against the sheet which, in its turn, is formed round or in the forming tool. When the sheet completely fits to the tool, the pressure in the pressure cell is released and the diaphragm is removed from the sheet, after which the formed component can be taken out of the press.
Another field in which presses of pressure cell type are used is wood compaction when a workpiece of wood is exposed to high pressure, either in a forming tool or on its own. Reasons for compacting wood are, for example, that it is desirable to increase the hardness of the wood, decrease the moisture content or to obtain a phase in pressure impregnation.
In traditional presses of pressure cell type, use has been made of a forged tray, in which at least the short sides of the tray are provided integrally with the bottom of a tray. The short sides and the radius transition to the bottom of the tray have to be dimensioned in such a manner that they can manage high working pressures. This means that the tray becomes unnecessarily thick and heavy.
SE 452 436 discloses a press of pressure cell type which was developed with the purpose of solving the above-mentioned problem. Said patent specification discloses a press plant having a forged, cylindrical press body which defines a press chamber. A tray which supports a forming tool and a workpiece is inserted into the press chamber. A large annular support which is arranged round the press body is adapted to absorb load being induced on the tray during a pressing operation. Each time the tray is to be taken out or inserted, the annular support has to be elevated in order to make the press chamber accessible. This is a complicated and time-consuming method.